CABELLO, A.; HAJTO, Z. Stratifications Adapted to Finite Families of Difierentíal 1-Forms (Pfafilan Geometry-PartOne). Revista Matemática Complutense, v. 8, n. 2, p. 269, 1 ene.1995 https://doi.org/10.5209/rev_REMA.1995.v8.n2.17643.